DESCRIPTION: A variety of experiments suggest that metabotropic glutamate receptors are important in sensory-dependent plasticity in the visual cortex. At the same time, metabotropic glutamate receptors have a variety of effects on the electrophysiological properties of cells in the visual cortex, and these have not been extensively studied. Presynaptic inhibition, postsynaptic excitation, and potentiation of the response to NMDA have all been shown to occur, but each has been studied in one layer of the cortex and not in others. Most likely these different effects occur because there are a variety of metabotropic glutamate receptors (defined by molecular biological techniques) located at different places in the cortex. Work with in situ hybridization, and with antibodies created against particular metabotropic glutamate receptors (defined by molecular biological techniques) located at different places in the cortex. Work with in situ hybridization, and with antibodies created against particular metabotropic glutamate receptors, shows that there are laminar differences in the distribution of these receptors, and these change with age. This application proposes to study the laminar differences and development of the electrophysiological effects of metabotropic glutamate receptors. The hypothesis is that these electrophysiological properties make it more likely that the postsynaptic cell will fire when the presynaptic cell fires at particular ages in development, leading to strengthening of synapses through a Hebbian mechanism, which may correlate with the critical period for sensory-dependent plasticity.